The present invention relates to technology for controlling a fuel injection quantity for an internal combustion engine equipped with a turbocharger. More particularly, the invention relates to technology for suppressing a supercharged pressure not to exceed an allowable upper limit even if a mechanism for adjusting the supercharged pressure is failed.
There has been known an internal combustion engine equipped with a turbocharger having a waste gate valve for controlling the supercharged pressure as disclosed in Japanese Unexamined Patent Publication No. 10-68327. That is, the waste gate valve is disposed in a passage bypassing a turbine of the turbocharger, and is opened to release the pressure when the supercharged pressure becomes excessive, so that the supercharged pressure is controlled at an allowable upper limit or below. In a turbocharger of electronically controlled variable nozzle type for controlling the supercharged pressure using a variable vane incorporated therein, an actuator that opens or closes the vane is controlled to control the supercharged pressure at the allowable upper limit or below.
When the waste gate valve or the actuator is failed due to fixing, however, the supercharged pressure is likely to exceed the allowable upper limit to become excessive, causing a damage to the internal combustion engine. Therefore, a fail-safe mechanism equipped with a relief valve has been proposed, for reducing the supercharged pressure by releasing an intake air into the open air when the supercharged pressure exceeds the allowable upper limit.
However, the relief valve is a fail-safe mechanism which operates only when the waste gate valve or the like is failed, and is, at present, an expensive component which should be abolished if there is available any other alternative means from the standpoint of fierce cost competition of present days.
In view of the above-mentioned conventional problems, it is an object of the present invention to provide a device for controlling a fuel injection quantity and a method of controlling the fuel injection quantity for an internal combustion engine equipped with a turbocharger, in which the fuel injection quantity is controlled according to the supercharged pressure, so that the supercharged pressure will not exceed an allowable upper limit even if a pressure adjustment mechanism is failed.
In order to accomplish the above-mentioned object, a device for controlling a fuel injection quantity for an internal combustion engine with a turbocharger according to the present invention, comprises:
failure judgment means for judging whether or not a mechanism for adjusting a supercharged pressure is failed;
normal time fuel injection quantity computing means for computing a fuel injection quantity of normal time based upon the engine operation condition when it is judged that the adjustment mechanism is not failed;
failed time fuel injection quantity computing means for computing a fuel injection quantity of failed time smaller than the fuel injection quantity of normal time based upon the engine operation condition when it is judged that the adjustment mechanism is failed; and
fuel injection control means for controlling the fuel injection based upon the computed fuel injection quantity of normal time or upon the computed fuel injection quantity of failed time.
On the other hand, a method of controlling a fuel injection quantity for an internal combustion engine with a turbocharger according to the present invention, comprises:
a failure judgment step of judging whether or a mechanism for adjusting a supercharged pressure is failed;
a normal time fuel injection quantity computing step of computing a fuel injection quantity of normal time based upon the engine operation condition when it is judged that the adjustment mechanism is not failed;
a failed time fuel injection quantity computing step of computing a fuel injection quantity of failed time smaller than the fuel injection quantity of normal time based upon the engine operation condition when it is judged that the adjustment mechanism is failed; and
a fuel injection control step of controlling a fuel injection based upon the computed fuel injection quantity of normal time or upon the computed fuel injection quantity of failed time.
According to this constitution, when the mechanism for adjusting the supercharged pressure is not failed, the fuel injection quantity is controlled based upon the fuel injection quantity of normal time. Therefore, the fuel injection quantity is controlled in a customary manner, and a driver does not feel it incompatible.
When the mechanism for adjusting the supercharged pressure is failed, on the other hand, the fuel injection quantity is controlled based upon the fuel injection quantity of failed time smaller than the fuel injection quantity of normal time. That is, the fuel injection quantity of normal time smaller than the fuel injection quantity of failed time is used, whereby the torque decreases and the engine rotational speed decreases. Since an intake air flow rate decreases with a decrease in the engine rotational speed, the supercharged pressure decreases so that it becomes possible to control the supercharged pressure at an allowable upper limit or below. Accordingly, the relief valve that was so far essential as a fail-safe mechanism can be abolished and, hence, achieving the decrease of cost, decrease of weight and improvement of reliability.
Further, in the device of the present invention, further, it is desired that the failed time fuel injection quantity computing means comprises:
first fuel injection quantity computing means for computing a first fuel injection quantity of when an accelerator is fully opened based upon the engine operation condition;
second fuel injection quantity computing means for computing a second fuel injection quantity smaller than the fuel injection quantity of normal time based upon the engine operation condition; and
fuel injection quantity selection means for selecting the smaller value between the first fuel injection quantity or the second fuel injection quantity as the fuel injection quantity of failed time.
In the method of the present invention, on the other hand, it is desired that the failed time fuel injection quantity computing step comprises:
a first fuel injection quantity computing step of computing a first fuel injection quantity of when an accelerator is fully opened based upon the engine operation condition;
a second fuel injection quantity computing step of computing a second fuel injection quantity smaller than the fuel injection quantity of normal time based upon the engine operation condition; and
a fuel injection quantity selection step of selecting the smaller value between the first fuel injection quantity or the second fuel injection quantity as the fuel injection quantity of failed time.
According to the above constitution, the smaller value between the first fuel injection quantity of when the accelerator is fully opened or the second fuel injection quantity smaller than the fuel injection quantity of normal time is used as the fuel injection quantity of failed time. Accordingly, once the adjustment mechanism is failed, the supercharged pressure is controlled at the allowable upper limit or below while maintaining smooth acceleration performance without the need of judging the occurrence of fault thereafter.
Moreover, in the device of the present invention, it is desired that supercharged pressure detecting means for detecting a supercharged pressure is provided, and the failure judgment means judges that the adjustment mechanism is failed when the detected supercharged pressure becomes equal to or greater than a predetermined value.
On the other hand, in the method of the present invention, it is desired that a supercharged pressure detecting step of detecting a supercharged pressure is provided, and the failure judgment step judges that the adjustment mechanism is failed when the detected supercharged pressure becomes equal to or greater than a predetermined value.
According to the above constitution, the failure in the pressure adjustment mechanism is judged based upon the supercharged pressure. Therefore, when for example, a supercharged pressure detecting means such as supercharged pressure sensor or the like is already provided, any sensor is not needed to be newly provided making it possible to suppress a rise in cost.
In addition, in the device of the present invention, it is desired that the normal time fuel injection quantity computing means and the failed time fuel injection quantity computing means compute the fuel injection quantity of normal time and the fuel injection quantity of failed time, respectively, by making a reference to a map in which the fuel injection quantity with respect to the engine operation conditions has been set.
On the other hand, in the method of the present invention, it is desired that the normal time fuel injection quantity computing step and the failed time fuel injection quantity computing step compute the fuel injection quantity of normal time and the fuel injection quantity of failed time, respectively, by making a reference to a map in which the fuel injection quantity with respect to the engine operation conditions has been set.
According to the above constitution, the fuel injection quantity of normal time and the fuel injection quantity of failed time are computed by making a reference to a map, suppressing an increase in the burden of processing that accompanies the computation of the fuel injection quantity.